Electric furnace



Patented Nov. 29, 1932 UNITED STATES PATENT OFFICE CLYDE R. JOHNSON, OF PRINCETON, NEW JERSEY, ASSIGNOR TO AMERSIL COMPANY,

INC., OF NEW YORK, N. Y., A CORPORATION OF NEW YORK ELECTRIC FURNACE Application filed September 9, 1931.

This invention relates to electric furnaces and it particularly relates to electric furnaces which are heated by the thermal effect of an electric current passing through a coil of resistance wire arranged on the outer surface of a chamber, constructed of electrically nonconductive material capable of withstanding the influence of a temperature 'of 'at least 1000 C. prevailing for a considerable length of time within said chamber. 7

It is one of the objects of the invention to create an electric furnace as a means to fuse substances, such as metals, and to have a considerable amount of fiat surface for a bed for the fused materials.

It is another object of my invention to create an electric furnace as a means to treat therein substances, for instance such as metals at an elevated temperature, including for instance temperatures at which the metals would fuse, and to have a clear vision of the inside of the furnace at all stages of the fusion or of any other action on the substance treated therein.

It is also an object of my invention to create an electric furnace as a means for fusing a number of different kinds of material in an atmosphere of various pure gases, corrosive (though not to the material of the chamber), or otherwise.

It is, furthermore, an object of my invention to create an electric furnace as a means for treating substances at an elevated temperature within a confined space, such as a chamber, having an unlubricated, but fairly tight, joint permitting operations within aforesaid confined space at a moderate pressure above or below that of the atmosphere and permitting easy access to the interior of the furnace.

It is thus obvious that my new electric furnace overcomes various shortcomings of the well known muffle furnace now universally used in chemical laboratories and factories. It is a long felt want that the mufiles of these furnaces, which are used from the smallest to very often considerable sizes, cannot be suitably closed so as to make them gas tight and to allow an easy access to its contents. These mufile furnaces are furthermore, always used Serial No. 561,828.

at very high temperatures and usually a door made of a cementitious material,.is arranged in front of the mufile opening to close the muflle, and the gap between the muflle and door is closed by some cement putty or other suitable material, but up to now no relief has been found from this situation which was cumbersome and unpleasant owing to the high temperatures applied. I

lVith these and other objects in view, which will be more apparent from the following description of my new invention, reference is had to the accompanying drawing, which illustrates by way of example one of the forms in which I may embody my new invention.

In said drawing:

Figure 1 is a horizontal sectional view through the electric furnace on the line 1-1 of Figure 2.

Figure 2 is a side elevation of the electric furnace, and

Figure 3 is a. detail view of the cap closing the electric furnace.

In said drawing the numeral 10 denotes the chamber of the furnace which consists of a body 11 and is made of fused silica. The form of this body 11 may vary within certain limits, for instance from that of a rectangular prism, as indicated in Figure 2 by the dashed line 12 and the bottom line 13, to that of a semi-cylinder, as indicated by the bottom line 13 and the curved line 14, which is the usual form of the well known muffle referred to above. In Figure 2 the dashed-dotted line 15 indicates another very suitable form of body for the chamber 10, which in its lower part is prismatic and is rounded at its, ceiling,,thus assuming the shape of a loaf of bread.

A neck 16 is secured to and preferably centrally arranged in the front side 17 of the body 11 so as to allow access to the inside of the same. This neck has preferably the form of a truncated cone so that the cap 18, which conforms with its inside shape to the outside shape of the neck 16 and which is ground in upon the same, closes the chamber 10 air-tight. While the mantle of the cap 18 is made of fused silica and therefore is opaque, the front side 19 is made of fused tiransparent quartz so as to serve as a win- A tube 20 is introduced into the inside of the chamber 10; it may be of any length, so as to terminate at any given point and preferably it is arranged close to the edge formed by the bottom 13 and the'curve'd ceiling l l: of the chamber 10. At the point where the tube 2O penetratesthe front side 17, a gas tight "point is made by'welding the "aforesaid front side 17 together with the peripheralcircumference of the tube 20. On the other side, opposite to the tube 20, a tubular neck'21is Welded to the front side 17 around anaperture so that this neck 21 may also communicate withthe inside space of chamber-10. Both tubeZO'an'd the tubular 'neck 2-1 are-of the same diameter andas they are provided, respectively, for the purpose-of introducing gases into and conducting them out of the chamber 10, their outer ends may beb'ent sidewardly to allow a more convenient "connection with other passageways of tubular or other form. v I v#It'vvill be noticed from an inspection of Figure 2 that the outside'diameter'of the'rim zof the neck 16 is practically identical with the height of the body 11. I

Though, in View of the negligible size of the c'oeflicient of expansion offused silica, there is no danger that the-ground joint be tween the neck 16 and the cap 18 will leak in case a moderate pressure is maintained with in the chamber 10, an annular cooling channel 22may be arranged around the cup l8 so that, in case very high temperatures are'apip'lied,zwater may flow through said channel 22 to absorb any heat which mightrcohtrib- 'uteto a slight expansion "so as to causea leak offsaidjoint.

'"As thebody '11 may be made of; a rectangular prismatic shape, the front side 17 is of considerable surface and in such case more than one neck16 with cap 18 maybe arranged sistancewire is arranged, which 'atits ends I 'isconnected with the bus-bars '(not shown) of a" source of electric "energy.

In case thebody 11" is for instance 14 cm.

' ber.

of 1000 C. As the mounting, of the essen- A tial parts of the electric furnace in asbestos insulation,' *eto.,= is Within @the knowledge of the art, illustration of these features is dispensed with.

It -1s cf"cou r-se-understood that I am not re- -'strieted to -theone transparent window 19 arranged in the cap 18, as I may arrange such winddws at any other suitable part of the body 11, for instance in the side 23 opposite to front side '17.

*The' operation --of ;the furnace --is self explanatory from the details givenaboveg; as one of the operations, for which the furnace was found toagive :a highly satisfactory'service, I cite the treatmentof-silVeunrrariged within the furnace-on -a suitable support, with :pure hydrogen -:gas., =FInthe absence-of rubber-gaskets, or-'meta-llic stoppers there is no possibility "of contaminating the: silver owing to the effect by the-hot corrosivejgases liberated during the :fusion.

What I claim is: v I V V,

In; an electric; furnace,--the combination comprising-a heating chamber made who'lly of fused silica and terminatingvat one side into-a tapered neck, a cap, of fused silicaand having a top "of transparent -quartz, ground in on" aforesaid neck so'asto' hermeticalily close aforesaidchamberflpirssa-gewziys for conducting al-g'as into and withdrawing same from aforesaidchamber, and'an electrically conductive resistance wire 'operati-vely arranged around thebody ofaforesaid cham- In witness "whereof I hereunto -set'- my hand. Y Y a GEYDE' 'R. I JOHNSONQ long,'8 crniwide and atom. high, and hasw'alls 7 3-4 mm. thick, the coil 24' is for instance Tna'de diameters of #16 (B. '& Sfga'uge) Chromel A';yvire,wrapped on an iron rod of 5 mm. and 'stretched'to' a length of 150 cm. whereupon it isrna'de to encirclethe body llfor a length of about 12 cm. Thefheating unit is intended for use on 110120 volt A. C. circuits,in se-Y 'r'ies'with an8' ohm', 8 ampere rheostat. The coils (only shown at both'ends) are carefully spaced and tied in position with'fasbefstos. Elh'fbody 11,"with'the open end ex'p'os'echfiis packed'in a (ine'gal'lon' crock linedwit-h magwho fos 

